Opposite: Negativity vs. Absence
Some people are fond of saying the opposite of love is indifference, not hate. This is an error. The opposite of any emotion is its counter emotion.
Joy is the opposite of sorrow.
Courage is the opposite of fear.
Indifference is the absence of any emotion.
Opposition is often confused with absence, and for good reason. A true opposite of anything is the negative of that thing. This is obvious with numbers. Five is the opposite of negative five, not the opposite of zero. That's why love is the opposite of hate, not indifference.
But some concepts don't have negatives, yet still appear to have opposites. Everyone knows the opposite of white is black - right? But white is light, and black is the absence of light - zero light. There is no negative light that we are aware of (though some physicist will undoubtedly propose it). Heat has no negative. Cold is simply the absence of it. Existence itself has no negative. There is only existence or non-existence - which is absence. We will always think of these things as opposites: white and black, hot and cold, existence and absence. We could call this a pseudo-opposite or acknowledge two kinds of opposites:
Opposite of absence
Does this mean we can call indifference the opposite (of absence) of love? Nobody can stop us, but if we do that, we will confuse things that have negatives with things that don't. If a concept has a negative, that thing should be recognized as its opposite.
A definition is in order:
Opposition is the relationship of two concepts on a common axis and equidistant from a midpoint on that axis. The axis represents a quality in which both concepts participate. e.g. An object in front of a mirror produces an image which is its opposite, the surface of the mirror being the midpoint. Acid is the opposite of alkaline, neutrality being the midpoint. Opposites cannot be identified without identifying that quality which is the criterion for opposition.
An opposite may be absolute or relative.
e.g. Three is the absolute opposite of minus three.
(zero being considered an absolute midpoint)
-4, -3, -2, -1, 0, 1, 2, 3, 4
An inward spiral is absolutely opposite in motion to an outward spiral.
(zero motion being considered an absolute midpoint)
e.g. France is opposite Germany relative to the Rhine River.
France is opposite Poland relative to Germany.
A particular black is the opposite of a particular white relative to a particular gray midpoint.
Hot is opposite cold only relative to a degree of heat arbitrarily regarded as neutral.
In any sequence of things, if one thing is arbitrarily taken as a midpoint, then if you count forward and backward from that thing any number of places, the resultant 2 things are opposite each other relative to that midpoint.
Some things simply don't have opposites. A line in one direction is the opposite of the same line going the other direction. But what is the opposite of a line? A point? A circle? A sphere? A line is a concept that has no opposite. If the absence of a line were the opposite of a line, then zero would be the opposite of anything and everything. But zero is the absence of anything and everything.
Evil is sometimes the opposite of good, and sometimes the absence of good. If it is good to do a particular act, not doing that act may be evil, or it may be morally neutral. If it is good to give money to a particular cause, not giving any money to that cause is not necessarily evil. Stealing money from the cause would be evil.